This program project is focused on characterizing the interaction between host and donor cells that affect post transplant events including rejection, graft versus host disease, graft versus leukemia, and immune reconstitution. These interactions are mediated via effector T-cells or NK cells bearing the receptors for MHC molecules and bound peptides. Therefore, the MHC molecules are pivotal characterizing the functions of their receptors on the effector cells. All the research projects proposed in this program utilize various cellular reagents than demand a clear definition of MHC repertoire. Molecular typing or clining of the HLA alleles (for transfection) requires technical expertise as well as specialized facilities. The establishment of this core is justified by a need to centralize HLA typing service, provide HLA DNA clones for transfection, and take quality measurement of all cellular reagents which will be used for the research projects. Specifically, this core will provide: 1) A comprehensive typing of HLA class I and class II alleles. The molecular HLA typing will be used for typing the cellular reagents, and also for quality assurance measurement of already HLA typing cell lines, transfectants, DNA clones, and also for the BMT patient's specimen for their chimeric status; 2) The plasmids that contains a full length cDNA of desired HLA alleles cloned in a mammalian expression vector. We will customize the HLA alleles for cloning as requested by each project. The core will maintain a stock of each cDNA clone and provide the quality controlled plasmid with enough qunatity for the establishment of transfectant. The quality of the cDNAs will be assessed by resstriction mapping, oligotyping, or sequencing for every batch of plasmid preparation; and 3) A technical assistance for making transfectants expressing HLA class I alleles. The core will provide the investigators the commonly used transfection host cells (K562, 721, CIR, T2, and P815), and also provide basic protocols for transfection. If and when requested, this core will assist in solving technical problems or in setting the optimal parameters for transfection.